Surface area of sphere: s = 4 π r squared.

2. Area of circle: S=π r square

Volume of sphere: V=4πR cubic /3.

3. The line between the center of the circle and the midpoint of the chord (not the radius) is perpendicular to the chord.

The straight line connecting the center of the sphere and the center of the section circle is perpendicular to the section.

4. Two chords with the same distance from the center of the circle are equal, while two chords with different distances from the center of the circle are different, and the chord closer to the center of the circle is longer.

The circular areas of cross sections with the same distance from the center of the sphere are equal.

Use first!